1. Field of the Invention
The present invention relates to a rotating machine with a rare earth sintered magnet and a method for producing a sintered magnet. More particularly to a sintered magnet with reduced amounts of heavy rare earth elements yet having a high energy product or high heat resistance and to a method.
2. Description of Related Art
The present invention relates to a sintered magnet and a rotating machine equipped with the sintered magnet, comprising an Fe-based magnet containing an R—Fe (where R represents a rare earth element); the sintered magnet includes a phase containing layered fluorine formed in grain boundary or within grains of the material of the Fe-based magnet in order to increase heat resistance of the Fe-based magnet containing the R—Fe, and the phase containing fluorine improves magnetic properties and reliability of the magnet. The magnet having the phase containing fluorine is used for a magnet having characteristics suitable for various types of magnetic circuits and magnet motors to which such magnets are applied. Such magnet motors include those magnet motors that are used for driving hybrid automobiles, and those magnet motors for starters and powered steering and so on in hybrid automobiles.
Conventional rare earth sintered magnets containing fluoride compounds or oxyfluoride compounds are disclosed in Patent Literature 1 (JP-A-2003-28312), Patent Literature 2 (JP-A-2006-303436), Patent Literature 3 (JP-A-2006-303435), Patent Literature 4 (JP-A-2006-303434), and Patent Literature 5 (JP-A-2006-303433). In the above-mentioned conventional technologies, the fluoride compounds used for processing are in the form of powder or mixtures of powder of respective compounds and a solvent, and it is difficult to efficiently form a phase containing fluorine along surfaces of magnetic particles. In the above-mentioned conventional methods, the fluoride compounds or oxyfluoride compounds used for the processing are in point contact with the surfaces of the magnetic particles, and it is difficult for the phase containing fluorine to come in surface contact with the magnetic particles unlike the method of the present invention. Therefore, there have been required a relatively large amount of the processing material and heat treatment at high temperatures according to the conventional methods. Patent Literature 6 (US2005/0081959A1) discloses a mixture of fine particles (1 to 20 μm) of a rare earth fluoride compound with Nd—Fe—B powder. However, it discloses no examples in which the Nd—Fe—B particles are grown such that they are discretely distributed in the form of plates. As described in Non-Patent Literature 1 (IEEE TRANSACTIONS ON MAGNETICS and VOL. 41 No. 10 (2005) Page 3844), fine particles (1 to 5 μm) of DyF3 or TbF3 are coated on the surface of a minute sintered magnet. This is done by a treatment other than the treatment with a solution of the fluoride compound but Dy and F are absorbed by the sintered magnet to form NdOF and Nd oxide. However, there is no description on the relationship between the concentration gradients of carbon, heavy rare earth, and light rare earth and the anisotropic direction of the magnet.    [Patent Literature 1] JP-A-2003-282312    [Patent Literature 2] JP-A-2006-303436    [Patent Literature 3] JP-A-2006-303435    [Patent Literature 4] JP-A-2006-303434    [Patent Literature 5] JP-A-2006-303433    [Patent Literature 6] US2005/0081959    [Non-Patent Literature 1] IEEE TRANSACTIONS ON MAGNETICS and VOL. 41 No. 10 (2005) Page 3844